With the proliferation of voltage regulator designs, manufacturers and suppliers of compatible voltage regulators are faced with high engineering and tooling costs to accommodate each distinct application. This situation is further complicated by the uncertainty of the need for a particular design, or whether an investment in any design will provide an adequate return. A solution to this dilemma is a design that fulfills a large number of different specialized requirements with a single circuit, with the further advantage of a one time investment in engineering and tooling costs.
One of the key objectives of this invention is a diversified circuit design that will accommodate a variety of voltage regulator applications without compromising individual quality or functionality of each application, while also enhancing reliability. An advantage of providing a single multi-application integrated circuit is that the probability of receiving a return of investment is greatly enhanced in that the cost can be amortized over a greater number of applications.
The following are prior United States patents which are pertinent to the present invention.
______________________________________ U.S. Pat. No. Issue Date Inventor ______________________________________ 4,143,313 3/1979 Arendt 4,266,181 5/1981 Muto et al. 4,315,205 2/1982 Muri et al. 4,360,773 11/1982 Voss 4,412,169 10/1983 Dell'Orto 4,435,676 3/1984 Morishita 4,459,489 7/1984 Kirk et al. 4,470,003 9/1984 Mitcheil 4,561,036 12/1985 Morishita et al. 4,563,631 1/1986 Mashino et al. 4,629,967 12/1986 Voss 4,629,968 12/1986 Butts et al. 4,636,705 1/1987 Bowman 4,636,706 1/1987 Bowman et al. 4,642,548 2/1987 Mashino 4,672,297 6/1987 Gotoh et al. 4,680,530 7/1987 Mashino 4,727,307 2/1988 Kaneyuki et al. 4,760,323 7/1988 Nadi 4,812,732 3/1989 Iwatani 4,831,322 5/1989 Mashino et al. 4,839,576 6/1989 Kaneyuki et al. 4,914,374 4/1990 Iwatani et al. 4,937,514 6/1990 Iwatani et al. 4,945,277 7/1990 Iwatani et al. ______________________________________
Attention is given to U.S. Pat. No. 4,636,706 to Bowman et al. This patent teaches a varible duty cycle field excitation waveform which is generated with a down counter periodically loaded with an up-down counter, and with the magnitude of the duty cycle being proportional to the "up" count in the up-down counter. The magnitude of the up count in the up-down counter is transferred into a down counter, the time it takes for the down counter to count down from its orignal value to zero being the duration of the "on" time that the field is excited in relation to the master cycle time.
In contrast, this invention uses a reversible counter in conjunction with a simple binary up counter with the up counter requiring fewer components than the down counter of the prior art. The magnitude of the field excitation is stored in the reversible counter as a down count, and the down count is transferred into the up counter. The time duration of the up counter counting up to zero determines the field excitation duty cycle.
As also discussed in the Bowman et al '706 patent, alternator speed control is obtained by a conventional frequency counter with a fixed time base circuit. This has the disadvantage of eroneously lighting the vehicle warning lamp for at least the duration of the fixed time base if the voltage regulator operation is interupted for some reason.
The circuit design of the present invention measures the time between the successive pulses provided by the alternator stator phase output. These time measurements are compared to a reference time to determine the speed of the alternator. As successive pulse measurement is incorporated, the time required for an accurate measurement is vastly shorter than the frequency counter, therefore, interruptions to this voltage regulator result in an imperceptible flashing of the warning lamp (in the order of microseconds) that is undetectable by the driver.
In the Bowman et al '706 patent, a linear series power supply which is switched on or off is used to provide reference voltages and digital circuit power. In this arrangement, the series pass transistor must absorb the excess voltage and voltage transients requiring a relatively large pass transistor. In switching the digital circuits on and off, inadvertent noise can simulate a switched condition, resetting the digital circuitry resulting in an erroneous flashing of the warning lamp.
In this invention, a shunt voltage regulator is used with the excess voltage and transients being absorbed by a resistor. The digital circuitry is designed using a "no false state allowed" rule that eliminates the need for a master reset. Thus, the circuit design of this invention only switches either on or off, only the peripheral input/output circuitry which unconditionally emulates the turn on or turn off characteristics of the prior art. With said digital circuitry operating continuously and with the lack of false states, this invention is immune to noise induced problems. As the digital circuitry is of CMOS construction the standby current requirements are essentially negligible.
In the Bowman et al, '706 patent, temperature compensation is accomplished with a chip external temperature compensation element. Such elements requiring trimming as an extra production item.
In contrast, this invention accomplishes temperature compensation of varying selectable slopes with a single "on-the-chip" diode. The characteristics of this diode are fixed in the mask of the chip, and avoid the requirement for trimming during manufacture. This diode is also used to shut down the peripheral drive circuits in the event that the alternator operational temperature exceeds a predetermined limit, thereby preventing catastrophic failure.
In the Bowman et al '706 patent, as with other of the cited patent references, a plurality of analog voltage comparators are used to accommodate the various functions required by each specific application. This plurality of comparators also requires individual trimming for each added comparator.
This invention uses a single analog comparator equipped with digitally switched inputs and outputs, which affords the advantage of having only one comparator to trim during the manufacturing operation. The scanning frequency of this comparator is substantially greater than the expected operational speed for any application of the voltage regulator, thereby producing an effective average voltage of each parameter measured. The Bowman et al circuit requires the use of separate analog and digital integrated circuits, whereas, this invention requires a single chip, representing a major saving in manufacturing costs.
The Bowman et al invention also requires different integrated circuits to accommodate different voltage regulator functions. This invention incorporates many different functions that can be selected by different wiring configurations of the respective data inputs. Thus, a relatively inexpensive change to the surface mount ceramic artwork need be only done to accommodate a variety of different applications.
Giving attention to U.S. Pat. No. 4,636,705 to Bowman, there is disclosed a complex voltage doubling scheme to provide the required biasing inherent to typical power MOSFET transistors.
This invention employs two high voltage on-chip FET transistors, three on-chip resistors, one diode, and one capacitor with a feed forward refresh pulse technique to provide adequate biasing required by a Power MOSFET transistor, which is achieved at far lower cost in terms of required circuit elements
Giving attention to U.S. Pat. No. 4,672,297 to Gotoh et al, this patent relates to the use of a single diode connected to the junction of the field winding and the field driver transistor. Moreover, by using this diode, an inadvertent short from the output of this diode to ground prevents a full field voltage condition that overexcites the alternator, causing possible damage to the vehicle's electrical loads. However, this diode is also subject to positive battery shorts, and this short condition is made more likely by the extensive use of non-conductive materials in the modern automobile. Such a short to a positive voltage conductor or terminal, either caused by wear or by the process of troubleshooting by an unaware mechanic, may cause excessive current to flow through the now forward-biased diode and through the field driver transistor. The magnitude of the current may be destructive to the field driver transistor, causing a flash through short, causing the damage that Gotoh intended to avoid.
This invention adds a redundant field driver FET transistor that inherently limits the shorted diode current to a safe value. As the addition of this redundant transistor isolates the main drive transistor from any accessible terminal, the shorting of the output diode either to ground or to the positive battery source allows the normal field driver circuitry to operate non-disturbed. As the added redundant FET field driver transistor has inherent current limiting, the removal of the inadvertent short would permit the operation of this circuit to return to normal with no damage.
Attention is given to U.S. Pat. No. 4,831,322 Mashino et al, which discloses another method for generating the high voltages required to operate an N-channel power MOSFET in the common source configuration. The technique disclosed by Mashino et al uses four capacitors, three diodes, a resistor, and five inverters to generate the bias voltage. This circuit is essentially a voltage doubler in which the output is buffered and gated with a ramp generator. This circuit also includes a complex feedback circuit consisting of a differential amplifier, a redundant field MOSFET with current sensing and associated components to track the field driver power MOSFET to the ramp generator. One disadvantage of a circuit of this type is that all the above components are operated at or near twice the battery voltage. If the effects of voltage transients are taken into consideration and in particular, in a vehicle where the battery terminals are corroded, the circuit is susceptible to high voltage breakdown unless expensive components were used. Further, in such a circuit arrangement, the bias voltage generation is independent of the field switching action.
In this invention, the bias voltage generation results directly from the field switch action, achieving a more efficient use of components. Only the essential components are operated at or near twice the battery voltage level to greatly lessen the probability of high voltage transient breakdown. The components that are operated at or near twice the battery voltage receive further protection by the inclusion of current limiting series resistors.